Method and system for image background suppression using neutral adjustment of color channels

ABSTRACT

Printing systems and methods are presented for image background and neutral adjustment of luminance-chrominance pixel values corresponding to a scanned image, in which white and black pixels are identified which have luminance values close to whitepoint and blackpoint values for the image, and which have chrominance values close to the chrominance neutral point. The chrominance values of these identified white and black pixels are selectively reduced based at least partially on proximity to the chrominance neutral point and chrominance of one or more neighboring pixels.

BACKGROUND

The present exemplary embodiment relates to document processing systemsand more particularly to neutral correction or adjustment of scannedimages. The disclosure finds particular utility in conjunction withbackground suppression in color scanning and copying systems and will bedescribed with a particular reference thereto. However, the exemplarytechniques and systems of this disclosure may alternatively be employedin other document processing systems and applications in whichbackground suppression is desired for images. In most copiers, anoriginal document is scanned by a digital scanner which converts thelight reflected from the document into electrical charges representingthe light intensity from predetermined areas (pixels) of the document,and is often characterized in a red-green-blue (RGB) color space.Background suppression may be applied in the original color space, orthe scanned image data can first be converted to a luminance/chrominancecolor space such as CIELab, where the luminance value L for each pixelrepresents the dark to light lightness dimension or luminosity, with “a”and “b” values representing the chrominance components in atwo-dimensional chrominance plane to define the difference between twodifferent colors of the same luminous intensity. Background adjustmentis often employed for improved rendering of scanned images in the scanand copy path of document processing systems such as color scanners andother multifunction devices, and is typically applied separately toluminance and chrominance channels of a set of luminance-chrominancepixel values corresponding to a scanned image. The pixels of image dataare then processed to convert the pixels of image data into signalswhich can be utilized by the digital reproduction machine to recreatethe scanned image. Background suppression is particularly advantageousto ensure that white regions in an original scanned document are imagedas white regions in a printed document, and is thus important to manycustomers. However, conventional background suppression techniques arelimited and there remains a need for improved methods and apparatus forimage background adjustment.

BRIEF DESCRIPTION

In the present disclosure, methods and systems are provided for imagebackground suppression in which neutral adjustment of color channels isused for both the light and dark ends of the luminance spectrum, and inwhich chrominance information for neighboring pixels is selectivelyemployed in adjusting pixels identified as being close to the whitepointand blackpoint values for an image. In the past, background adjustmenthas been performed separately for the luminance and chrominancechannels, and conventionally did not take into account the dark end ofthe luminance spectrum or the chrominance of neighboring pixels. Thepresent disclosure may advantageously be employed in document processingsystems and other applications in which scanned image data is to bereproduced to facilitate improved background adjustment whilemaintaining neutrality in the light and dark areas of the document.

Image background adjustment methods are provided in accordance withcertain aspects of the disclosure, in which image luminance andchrominance values are received along with whitepoint and blackpoint(offset) value corresponding to an image, with white and black pixelsbeing identified based on luminance value proximity to the whitepoint orblackpoint as well as on the chrominance proximity to the neutral pointin the chrominance space. White pixels are identified as those scannedpixels having luminance values within a white offset value of thewhitepoint value, as well as having chrominance values within a non-zerowhite chrominance threshold value of the chrominance neutral point.Similarly, the method includes identifying black pixels having luminancevalues within a black offset value of the blackpoint value and havingchrominance values within a non-zero black chrominance threshold valueof the neutral point that is less than the white chrominance thresholdin certain embodiments. The method further provides for adjustingbackground pixels by selectively reducing the chrominance values (a, b)of the identified white and black pixels based at least partially onproximity to the chrominance neutral point and chrominance of at leastone neighboring pixel.

In certain embodiments, the chrominance values are selectively set tothe neutral point for identified white and black pixels with chrominancevalues within a chrominance adjustment threshold of the chrominanceneutral point, where the chrominance adjustment threshold is less thanthe white and black chrominance threshold values, and the chrominance isselectively reduced by an amount equal to either the chrominanceadjustment threshold or the average deviation from the neutral point forthe remaining white and black pixels for which at least one neighboringpixel is an identified white or black pixel, respectively. In certainembodiments, moreover, the method provides for selectively furtheradjusting the chrominance values of at least one of the identified whiteand black pixels based on adjusted chrominance values of neighboringpixels.

Other aspects of the disclosure involve document processing systems thatinclude a scanning component that produces a red-green-blue color pixelrepresentation of an original image, a color space converter thatconverts values of red-green-blue pixels into correspondingluminance-chrominance pixel values, and a white and black pixelidentification component. The identification component identifies whitepixels as those pixels having luminance values within a white offsetvalue of a whitepoint value associated with the image and havingchrominance values within a non-zero white chrominance threshold valueof a chrominance neutral point, and black pixels having luminance valueswithin a black offset value of a blackpoint value associated with theimage and having chrominance values within a non-zero black chrominancethreshold value of the chrominance neutral point. A chrominanceadjustment component is provided to selectively reduce chrominancevalues of the identified white and black pixels based at least partiallyon proximity to the chrominance neutral point and chrominance of atleast one neighboring pixel, as well as a memory for storing originaland adjusted pixel values corresponding to the image.

BRIEF DESCRIPTION OF THE DRAWINGS

The present subject matter may take form in various components andarrangements of components, and in various steps and arrangements ofsteps. The drawings are only for purposes of illustrating preferredembodiments and are not to be construed as limiting the subject matter.

FIG. 1 is a schematic system level diagram illustrating an exemplarydocument processing system with a white and black pixel adjustmentcomponent and a chrominance value adjustment component in accordancewith various aspects of the present disclosure;

FIG. 2 is a schematic diagram illustrating a single dimensional 5×1neighboring pixel window that may be employed in certain embodiments ofthe system of FIG. 1;

FIG. 3 is a schematic diagram illustrating a multi-dimensional 3×3neighboring pixel window that may be employed in embodiments of thesystem of FIG. 1;

FIG. 4 is a schematic diagram illustrating an exemplary CIELabluminance-chrominance color space with white and black pixel offsetvalues and a chrominance neutral point;

FIG. 5 is a flow diagram illustrating an exemplary background adjustmentmethod in accordance with certain aspects of the present disclosure; and

FIGS. 6A-6F depict a flow diagram illustrating another exemplarybackground adjustment method in accordance with the disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 illustrates an exemplary documentprocessing or printing system 10 in accordance with one or more aspectsof the present disclosure. The printing system 10 can be any form ofcommercial printing apparatus, copier, printer, facsimile machine, orother system having a scanner or other input device 12 that scans anoriginal document text and/or images to create an image comprising pixelvalues indicative of the colors and/or brightness of areas of thescanned original, and which preferably includes one or more markingengines or print engines 14 by which visual images, graphics, text, etc.are printed on a page or other printable medium, including xerographic,electro photographic, and other types of printing technology, whereinsuch components are not specifically illustrated to avoid obscuring thevarious alternate imaging features of the present disclosure. The printengine 14 may be any device or marking apparatus for applying an imagefrom a printer controller 16 to printable media (print media) such as aphysical sheet of paper, plastic, or other suitable physical mediasubstrate for images, whether precut or web fed, where the input device12, print engine 14, and controller 16 are interconnected by wiredand/or wireless links for transfer of electronic data in between,including but not limited to telephone lines, computer cables, ISDNlines, etc. The print engine 14 generally includes hardware and softwareelements employed in the creation of desired images byelectrophotographic processes wherein suitable print engines may alsoinclude ink-jet printers, such as solid ink printers, thermal headprinters that are used in conjunction with heat sensitive paper, andother devices capable of printing an image on a printable media.

The image input device 12 may include conversion components forconverting the image-bearing documents to image signals or pixels orsuch function may be assumed by the marking engine 14. In theillustrated embodiment, for example, the system 10 includes an analyzercomponent 18, which can be any suitable hardware, software, logic, orcombinations thereof, whether implemented as a single component or asmultiple interoperative components, that is comprised of an RGB-to-Labconverter 126, a white and black pixel identification component 140, abackground pixel value memory 116, a suppression component 20 with achrominance adjustment component 160, and a pixel memory 180 for storingoriginal and adjusted pixel values corresponding to an input image. Inthis embodiment, the image input device 12 may be used to scan anoriginal document to form red-green-blue (RGB) values, and the RGB toLab converter component 126 converts the RGB data to CIELab pixel datahaving luminance (L) and chrominance (a, b) values for each pixel of thescanned image, where L represents the luminance/lightness component anda, b are the chrominance values. The identification component 140receives the Lab input values and identifies certain of these as whiteor black pixels using whitepoint, blackpoint, and white and black offsetvalues stored in the background pixel memory 116. The chrominance valueadjustment component of the background suppression system 20 performsselective, adaptive background adjustment as illustrated and describedfurther hereinafter with respect to FIGS. 5 and 6A-6E.

The illustrated printing engine 14 is fed with a print media sheets 22from a feeding source 24 such as a paper feeder which can have one ormore print media sources or paper trays 26, 28, 30, 32, each storingsheets of the same or different types of print media 22 on which themarking engine 14 can print. The printing engine 14 includes an imagingcomponent 44 and an associated fuser 48, which may be of any suitableform or type, and may include further components which are omitted fromthe figure so as not to obscure the various aspects of the presentdisclosure. For instance, the printing engine 14 may include aphotoconductive insulating member which is charged to a uniformpotential and exposed to a light image of an original document to bereproduced. The exposure discharges the photoconductive insulatingsurface in exposed or background areas and creates an electrostaticlatent image on the member corresponding to image areas of the originaldocument. The electrostatic latent image on the photoconductiveinsulating surface is made visible by developing the image with animaging material such as a developing powder comprising toner particles,which is then transferred to the print media and permanently affixed inthe fusing process. In a multicolor electrophotographic process,successive latent images corresponding to different colors can be formedon the insulating member and developed with a respective toner of acomplementary color, with each color toner image being successivelytransferred to the paper sheet in superimposed registration with theprior toner image to create a multi-layered toner image on the printedmedia 22, and where the superimposed images may be fusedcontemporaneously, in a single fusing process. The fuser 48 receives theimaged print media from the image-forming component and fixes the tonerimage transferred to the surface of the print media 22, where the fuser48 can be of any suitable type, and may include fusers which apply heator both heat and pressure to an image. Printed media from the printingengine 14 is delivered to a finisher 36 including one or more finishingoutput destinations 38, 40, 42 such as trays, stackers, pans, etc.

The document processing system 10 is operative to perform these scanningand printing tasks in the execution of print jobs, which can includeprinting selected text, line graphics, images, machine ink characterrecognition (MICR) notation, etc., on either or both of the front andback sides or pages of one or more media sheets 22. An original documentor image or print job or jobs 50 can be supplied to the printing system10 in various ways. In one example, the built-in optical scanner 12 maybe used to scan a document such as book pages, a stack of printed pages,or so forth, to create a digital image of the scanned document that isreproduced by printing operations performed by the printing system 10.Alternatively, the print jobs can be electronically delivered to thesystem controller 16 via a network or other means, for instance, wherebya network user can print a document from word processing softwarerunning on a network computer, thereby generating an input print job.

In the system 10, moreover, a print media transporting system or networkor highway 60 links the print media source 24, the print or markingengine 14 and a finisher 36 via a network of flexible automaticallyfeeding and collecting drive members, such as pairs of rollers 62,spherical nips, air jets, or the like, along with various motors for thedrive members, belts, guide rods, frames, etc. (not shown), which, incombination with the drive members, serve to convey the print mediaalong selected pathways at selected speeds. In the example of FIG. 1,print media 22 is delivered from the source 24 to the print engine 14via a pathway 64 common to the input trays 26, 28, 30, 32, and isprinted by the imaging component 44 and fused by the fuser 48, with apathway 68 from the printer 14 merging into a pathway 74 which conveysthe printed media to the finisher 36, where the pathways 64, 68, 74 ofthe network 60 may include inverters, reverters, interposers, bypasspathways, and the like as known in the art. In addition, the printengine 14 may be configured for duplex or simplex printing and a singlesheet of paper 22 may be marked by two or more print engines 14 or maybe marked a plurality of times by the same marking engine 14, forinstance, using internal duplex pathways.

Referring also to FIGS. 2-5, in accordance with various aspects of thepresent disclosure, the document processing system 10 includes animproved analyzer component 18 for image background suppression of thechrominance channels which employs selective neutral adjustment in thewhite and black areas of a scanned image using chrominance informationfor neighboring white and black pixels. The neighboring pixels can beanalyzed according to any suitable neighboring pixel window of size m×n,where m is an integer greater than or equal to two and n is an integergreater than or equal to one. FIG. 2 illustrates one exemplary singledimensional 5×1 neighboring pixel window 200 that may be employed incertain embodiments of the system of FIG. 1, including the pixel ofinterest “X” 206 as well as two neighboring pixels A, B 202 and 204 andC, D 208 and 210 on either side of the pixel 206. An exemplarymulti-dimensional 3×3 neighboring pixel window 220 is shown in FIG. 3,including neighbor pixels A-H 222, 224, 226, 228, 232, 234, 236, and 238surrounding the pixel of interest 230.

FIG. 4 illustrates an exemplary CIELab luminance-chrominance color space230 with orthogonal L, a, and b axes, including exemplary whitepoint andblackpoint values (whitepointL and blackpointL) with predefined orsystem programmable white and black pixel offset values (whiteoffsetLand blackoffsetL) and a chrominance neutral point (NEUTRALA, NEUTRALB).In one example, NEUTRALA and NEUTRALB are programmable according to theluminance-chrominance space being utilized, such as 128 for bothNEUTRALA and NEUTRALB for CIELab and YCbCr images, whereas for FAXLABimages these values could be 128 and 96.

The exemplary analyzer 18 in one example uses pre-determined whitepointand blackpoint values whitepointL and blackpointL, which are luminancechannel offsets for a given image, which can be provided with a scannedor input image, or which can be determined by the analyzer 18 using anysuitable technique. In particular, the programmable offsets whiteoffsetLand blackoffsetL define luminance ranges or bands around the valueswhitepointL and blackpointL used by the system 10 to identify white andblack pixels, where the offsets whiteoffsetL and blackoffsetL may butneed not be equal to one another.

The analyzer 18 operates generally in accordance with the method 250 ofFIG. 5 to suppress background in the color channels a and b thus makingthem more neutral without affecting the color of non-background areas,using an adaptive technique according to the amount of deviation of theneighboring pixels from the neutral point. While the exemplary method250 and other methods are illustrated and described hereinafter in theform of a series of acts or events, it will be appreciated that thevarious methods in the claims below are not limited by the illustratedordering of such acts or events except as specifically set forththerein. In this regard, except as specifically provided in the claims,some acts or events may occur in different order and/or concurrentlywith other acts or events apart from those acts and ordering illustratedand described herein, and not all illustrated steps may be required toimplement a process or method in accordance with the present disclosure.The methods, moreover, may be implemented in hardware, software, orcombinations thereof, in order to provide the described functionality,wherein these methods can be practiced in hardware and/or software ofthe above described systems or other hardware and/or softwareoperatively associated with a printing system, wherein the disclosure isnot limited to the specific applications and implementations illustratedand described herein.

The method 250 begins in FIG. 5 with receipt at 252 by theidentification component 140 of luminance-chrominance pixel values (Lab)for the document imaged by the scanner 12. The identification component140 utilizes the whitepoint value whitepointL and the blackpoint valueblackpointL corresponding to the scanned image, and processes the pixeldata sequentially beginning with a first pixel at 254. In operationaccording to the process 250, the identification component 140identifies each pixel as white or black or neither according to thepixel luminance and chrominance at 256 and 257, and for white and blackpixels, the chrominance adjustment component 160 of the backgroundsuppression system 20 performs selective chrominance reduction at 260.In particular, a determination is made at 256 as to whether the currentpixel luminance value L is close to the whitepoint or blackpoint valuesand if so, whether the pixel chrominance is close to the neutral point.If not (NO at 256), no adjustment is done, and a determination is madeat 257 as to whether more pixels remain. If so (YES at 257), theanalyzer 18 gets the next pixel at 258 and proceeds to 256.

In one implementation of the proximity testing at 256, theidentification component 140 identifies white pixels as those that haveluminance values L within a white offset value whiteoffsetL of thewhitepoint value whitepointL (e.g., L is greater than or equal towhitepointL−whiteoffsetL) and which have chrominance values a and bwithin a non-zero white chrominance threshold value of the chrominanceneutral point NEUTRALA, NEUTRALB. Similarly, the component 140identifies black pixels at 256 as those having luminance values L withinthe black offset value blackoffsetL of the blackpoint value and havingchrominance values a and b within a black chrominance threshold value ofthe chrominance neutral point, where the white and black thresholdvalues may be the same or the white chrominance threshold value isgreater than the black chrominance threshold value in one possibleembodiment.

If the current pixel luminance is close to the whitepoint or blackpointand the pixel chrominance is near the neutral point (YES at 256), thecurrent pixel is classified or identified as a white or black pixel at259, and the method 250 proceeds to 260 where the chrominance adjustmentcomponent 160 (FIG. 1) selectively reduces the chrominance values a andb based at least partially on proximity to the chrominance neutral pointNEUTRALA, NEUTRALB and chrominance of at least one neighboring pixel. Adetermination is made at 262 as to whether the chrominance of theidentified white or black pixel is within a tighter range or band closeto the chrominance neutral point, where the chrominance adjustmentthreshold is less than the white chrominance threshold value and alsoless than the black chrominance threshold value. If so (YES at 262), thechrominance values a and b are adjusted to the neutral point valuesNEUTRALA and NEUTRALB, respectively, at 263, and the process returns todetermine if further pixels remain at 257 as described above. In oneimplementation at 262, the adjustment component determines if theidentified white or black pixel has chrominance values within achrominance adjustment threshold of the chrominance neutral pointNEUTRALA, NEUTRALB, and if so, adjusts the chrominance values at 263 tothe neutral point (a is set to NEUTRALA, and b is set to NEUTRALB).

For remaining identified white and black pixels with chrominance valuesnot within the chrominance adjustment threshold of the neutral point (NOat 262), the adjustment component 140 determines at 264 whether thepixel of interest has any white or black neighbor pixels. If not (NO at264), no adjustment is made to the current pixel and the process returnsto 257 as described above. Otherwise (YES at 264), the component 140analyzes the chrominance of neighboring white or black pixels at 266 andselectively reduces the chrominance values a and b at 268 based on thechrominance of neighboring white or black pixels.

Once all the pixels have been processed (NO at 257), these are stored inmemory (e.g., in the pixel memory 180 in FIG. 1), and the chrominance ofidentified black and white pixels can optionally be selectively furtheradjusted at 270 (reduced closer to the neutral point) based on adjustedchrominance values of neighboring pixels. In one implementation, thefurther adjustment at 270 includes adjusting the chrominance values aand b to the chrominance neutral point NEUTRALA and NEUTRALB,respectively, if the adjusted chrominance values of all the neighboringpixels are at the chrominance neutral point. In other possibleembodiments, moreover, the selective further adjustment at 270 may beperformed earlier, such as once the chrominance of all the pixels in thespecified neighborhood have been adjusted in order to conserve memoryusage in the analyzer 18. A further optional adjustment may be performedat 272, in which the chrominance values a and b for the pixels areselectively further adjusted to the chrominance neutral point NEUTRALA,NEUTRALB if the adjusted chrominance values are within one of thechrominance neutral point values NEUTRALA, NEUTRALB. Thereafter,luminance may be adjusted at 274 using any suitable techniques.

FIGS. 6A-6F provide a flow diagram 300 illustrating another exemplaryselective and adaptive background adjustment method in accordance withthe present disclosure, which may be implemented, for example, in thedocument processing system 10 of FIG. 1. An image is scanned orotherwise input at 302 (e.g. 1 via scanner 12 in FIG. 1), and theresulting RGB values are formed at 304 and stored in memory. These arethen converted at 306 into Lab values, and the image whitepoint andblackpoint values (whitepointL and blackpointL) are detected orotherwise determined using any suitable techniques as are known.

At 310, the first Lab pixel is evaluated or analyzed with adetermination being made at 312 as to whether the pixel luminance valueL is near to the whitepoint (e.g., whether L≧(whitepointL−whiteoffset),where the whiteoffset in one example is about 10 for CIELab and isprogrammable. If not (NO at 312), the pixel is not identified as a whitepixel and the process continues to determine whether the current pixelis to be classified as a black pixel at 322 as described below. If theluminance value L is within whiteoffset of the whitepoint (YES at 312),a determination is made at 314 as to whether the chrominance values aand b are within a white chrominance threshold TH1 of the neutral point(e.g., whether |(a−NEUTRALA)|<TH1, and |(b−NEUTRALB)|<TH1). If not (NOat 314), the process 300 continues at 330 with no adjustment to thepixel chrominance values a or b, the next pixel is retrieved and themethod 300 returns to 312 as described above. If, however, the pixelluminance L is close to the whitepoint (YES at 312) and the pixelchrominance values a and b are sufficiently close to the neutral point(YES at 314), the pixel is identified as white at 316 and the method 300continues at 340 in FIG. 6B as further described below.

If the current pixel is not sufficiently close to the whitepoint (NO at312), a determination is made at 322 as to whether the pixel luminance Lis within a black offset value blackoffset of the image black point(e.g., whether L≦(blackpointL+blackoffset). In one possible embodiment,the black offset value is programmable, and in another example has avalue in the range of about 20 to 30. If not, (NO at 322), the pixel isnot identified as a black pixel, and the process continues at 330 withno adjustment to the pixel chrominance values a or b, the next pixel isretrieved, and the method 300 returns to 312 as described above. If thepixel luminance L is within the programmable range of the blackpoint(YES at 322), a determination is made at 324 as to whether the pixelchrominance values a and b are within a black chrominance threshold TH3of the neutral point (e.g., whether |(a−NEUTRALA)|<TH3, and|(b−NEUTRALB)|<TH3). If not (NO at 324), the process proceeds to thenext pixel with no chrominance adjustment at 330 and 312 as describedabove. In an alternative embodiment, for pixels not identified as whiteor black (NO at 314, 322, or 324), the process 300 proceeds to 325 asdescribed further below. Otherwise (YES at 324), the pixel is identifiedas black at 326 and the method 300 continues at 350 in FIG. 6B asdescribed in greater detail below. In the exemplary implementation, thewhite and black chrominance thresholds are non-zero, with the whitethreshold TH1 being greater than the black threshold TH3, although otherembodiments are possible using any suitable non-zero, positivethresholds TH1 and TH3, which may, but need not, be equal.

Turning now to FIG. 6B, the chrominance values a and b of pixelsidentified as white or black pixels are further compared to a narrowerthreshold range about the neutral point using a programmable chrominanceadjustment threshold TH2 for selective chrominance adjustment(reduction) based on proximity to the neutral point (NEUTRALA, NEUTRALB)or on the chrominance of neighboring pixels. In one possible embodiment,TH2 is less than TH1 and also less than TH3, although otherimplementations are contemplated as falling within the scope of thepresent disclosure. For white pixels, the process 300 proceeds at 340where a determination is made as to whether the chrominance values a andb are within the chrominance adjustment threshold TH2 of the neutralpoint (whether |(a−NEUTRALA)|<TH2, and |(b−NEUTRALB)|<TH2). If so (YESat 340), the pixel chrominance is adjusted to the neutral point at 342(a is set to NEUTRALA, and b is set to NEUTRALB), and the process 300returns to 312 in FIG. 6A to analyze the next pixel. Otherwise (NO at340), the white pixel chrominance adjustment process 300 proceeds to 360in FIG. 6C as described further below. Continuing in FIG. 6B, adetermination is made for black pixels at 350 as to whether thechrominance values a and b are within the chrominance adjustmentthreshold TH2 of the neutral point, and if so (YES at 350), the blackpixel chrominance is adjusted to the neutral point at 352, and theprocess 300 returns to 312 in FIG. 6A to analyze the next pixel. If not(NO at 350), the adjustment process 300 proceeds to 400 in FIG. 6E asdescribed further below.

Referring now to FIG. 6C, for white pixels having chrominance outsidethe chrominance adjustment threshold TH2, the neighboring pixels areassessed at 360 with a determination being made at 362 as to whether anyneighbor pixels are white. If not (NO at 362), the process 300 returnsto 330 in FIG. 6A to get the next pixel with no chrominance adjustmentto the current pixel as described above. If instead there is at leastone neighboring white pixel (YES at 362 in FIG. 6C), chrominance valueoffsets are calculated at 364 for the a and b channels for theneighboring pixels classified as white, as well as the current pixel asdeviations from the neutral point (OFFSETA=|a−NEUTRALA|, andOFFSETB=|b−NEUTRALB|), and an average offset is computed at 366 for eachchrominance channel (avgA and avgB). For the first chrominance channel“a”, a determination is then made at 368 as to whether the pixel a valueis greater than the neutral point (e.g. whether a>NEUTRALA). If so (YESat 368), the chrominance “a” value is selectively offset toward theneutral point by an amount equal to the chrominance adjustment thresholdor to the average white neighboring pixel “a” channel offset computed at366. A determination is made at 370 as to whether|(a−avgA−NEUTRALA)|>|(a−TH2−NEUTRALA)|. If so (YES at 370), a pixeloffset is set to −TH2 at 372, and otherwise (NO at 370), the offset isset to −avgA at 374, after which the “a” value is adjusted at 376 by theoffset amount (a_new=a+offsetA). The pixel “a” value is similarlyadjusted toward the neutral point NEUTRALA for cases where a is lessthan the neutral (NO at 368 above), where a determination is made at 380as to whether |(a+avgA−NEUTRALA)|>|(a+TH2−NEUTRALA)|. If so (YES at380), a pixel offset is set to TH2 at 382, and otherwise (NO at 380),the offset is set to avgA, after which the “a” value is adjusted at 376by the offset amount (a_new=a+offsetA).

Referring also to FIG. 6D, following the selective “a” channelchrominance adjustment at 376, the process continues to 390 in FIG. 6Dfor adjustment of the “b” channel chrominance value. At 390, adetermination is made as to whether the “b” channel chrominance exceedsthe neutral point (b>NEUTRALB). If so (YES at 390), the “b” channelchrominance value is selectively offset toward the neutral point by anamount equal to the chrominance adjustment threshold or to the averagewhite neighboring pixel “a” channel offset computed at 366 in FIG. 6C. Adetermination is made at 391 in FIG. 6D as to whether|(b−avgB−NEUTRALB)|>|(b−TH2−NEUTRALB)|. If so (YES at 391), a pixeloffset is set to −TH2 at 392, and otherwise (NO at 391), the offset isset to −avgB at 393. Thereafter, the “b” value is adjusted at 394 by theoffset amount (b_new=b+offsetB). For cases where b is less than theneutral (NO at 390), the pixel “b” value is similarly adjusted towardthe neutral point NEUTRALB, where a determination is made at 396 as towhether |(b+avgB−NEUTRALB)|>|(b+TH2−NEUTRALB)|. If so (YES at 396), apixel offset is set to TH2 at 397, and otherwise (NO at 396), the offsetis set to avgB, after which the “b” value is adjusted at 394 by theoffset amount (b_new=b+offsetB).

Once the a and b channel chrominance values have been adjusted for thewhite pixel at 376 and 396 in FIGS. 6C and 6D, respectively, theadjusted values are stored in the pixel memory (memory 180 in FIG. 1),the process 300 continues to get the next pixel at 395, and returns foradjustment processing at 312 in FIG. 6A as described above. Similarprocessing is undertaken for black pixels to selectively adjust thechrominance based on chrominance of neighboring black pixels. Referringto FIGS. 6B and 6E, for indentified black pixels with chrominance valuesnot within the chrominance adjustment threshold TH2 of the neutral point(NO at 350 in FIG. 6B), the adjustment process 300 proceeds to assessneighbor pixels at 400 in FIG. 6E, where a determination is made at 402as to whether any neighbor pixels are black. If not (NO at 402), theprocess 300 returns to 330 in FIG. 6A as previously described to get thenext pixel with no chrominance adjustment to the current pixel.Otherwise (there is at least one neighboring black pixel, YES at 402 inFIG. 6E), a and b channel chrominance value offsets are calculated forthe neighboring pixels classified as black as well as the current pixelat 404 as deviations from the neutral point (OFFSETA=|a−NEUTRALA|, andOFFSETB=|b−NEUTRALB|), and average offset values avgA and avgB arecomputed at 406 for each chrominance channel. Thereafter, the selectivechrominance adjustment is undertaken for the black pixels as describedabove in connection with FIGS. 6C and 6D beginning at 368 in FIG. 6C,with the adjusted chrominance values a and b being stored along with theluminance value L in the pixel memory 180 of FIG. 1.

Referring now to FIGS. 6A and 6F, if the current pixel is not identifiedas white or black (NO at 314, 322, or 324 in FIG. 6A), a determinationis made at 325 as to whether the current pixel chrominance values (a, b)are within a still narrower chrominance threshold TH4 of the neutralpoint (|(a−NEUTRALA)|<TH4, and |(b−NEUTRALB)|<TH4), where the narrowchrominance threshold TH4 in one embodiment is less than or equal to thechrominance threshold TH2 to avoid highlight clipping and not to changecolors. If not (NO at 325), no adjustment is made to the current pixelchrominance, and the process proceeds to get the next pixel at 330 asdescribed above. Otherwise (YES at 325 in FIG. 6A), the process 300proceeds to selectively adjust the chrominance based on neighboringpixels in FIG. 6F. In this case, the non-white or black pixelchrominance adjustment includes assessing the neighboring pixels at 410with a determination being made at 412 as to whether at least two of theneighboring pixels are also within the narrow chrominance threshold TH4of the chrominance neutral point white (|(a−NEUTRALA)|<TH4, and|(b−NEUTRALB)|<TH4), and the neighboring pixel luminance L is within acertain threshold TH5 of the current pixel luminance(|(L_(NEIGHBOR)−L_(CURRENT PIXEL))|<TH5). If not (NO at 412), theprocess 300 returns to 330 in FIG. 6A to get the next pixel with nochrominance adjustment to the current pixel as described above.Otherwise (YES at 412 in FIG. 6F), chrominance value offsets arecalculated at 414 for the a and b channels for the current pixel and forsuch neighboring pixels as deviations from the neutral point(OFFSETA=|a−NEUTRALA|, and OFFSETB=|b−NEUTRALB|). An average offset iscomputed at 416 for each chrominance channel (avgA and avgB), and theprocess 300 proceeds to 368 in FIG. 6C whereafter selective chrominanceadjustment is undertaken for the current (non-white and non-black) pixelas described above in connection with FIGS. 6C and 6D, with the adjustedchrominance values a and b being stored along with the luminance value Lin the pixel memory 180 of FIG. 1.

The above examples are merely illustrative of several possibleembodiments of the present disclosure, wherein equivalent alterationsand/or modifications will occur to others skilled in the art uponreading and understanding this specification and the annexed drawings.In particular regard to the various functions performed by the abovedescribed components (assemblies, devices, systems, circuits, and thelike), the terms (including a reference to a “means”) used to describesuch components are intended to correspond, unless otherwise indicated,to any component, such as hardware, software, or combinations thereof,which performs the specified function of the described component (i.e.,that is functionally equivalent), even though not structurallyequivalent to the disclosed structure which performs the function in theillustrated implementations of the disclosure. In addition, although aparticular feature of the disclosure may have been disclosed withrespect to only one of several embodiments, such feature may be combinedwith one or more other features of the other implementations as may bedesired and advantageous for any given or particular application. Also,to the extent that the terms “including”, “includes”, “having”, “has”,“with”, or variants thereof are used in the detailed description and/orin the claims, such terms are intended to be inclusive in a mannersimilar to the term “comprising”. It will be appreciated that various ofthe above-disclosed and other features and functions, or alternativesthereof, may be desirably combined into many other different systems orapplications, and further that various presently unforeseen orunanticipated alternatives, modifications, variations or improvementstherein may be subsequently made by those skilled in the art which arealso intended to be encompassed by the following claims.

1. A method of image background adjustment, the method comprising:receiving luminance-chrominance pixel values, a whitepoint value, and ablackpoint value which correspond to an image; identifying white pixelshaving luminance values within a white offset value of the whitepointvalue and having chrominance values within a non-zero white chrominancethreshold value of a chrominance neutral point; identifying black pixelshaving luminance values within a black offset value of the blackpointvalue and having chrominance values within a non-zero black chrominancethreshold value of the chrominance neutral point; and adjusting pixelsby selectively reducing the chrominance values of the identified whiteand black pixels based at least partially on proximity to thechrominance neutral point and chrominance of at least one neighboringpixel.
 2. The method of claim 1, wherein the white chrominance thresholdvalue is greater than the black chrominance threshold value.
 3. Themethod of claim 1, wherein selectively reducing the chrominance valuesof the identified white and black pixels comprises: for identified whiteand black pixels with chrominance values within a chrominance adjustmentthreshold of the chrominance neutral point, adjusting the chrominancevalues to the chrominance neutral point, the chrominance adjustmentthreshold being less than the white chrominance threshold value and lessthan the black chrominance threshold value; for remaining identifiedwhite pixels with chrominance values not within the chrominanceadjustment threshold of the chrominance neutral point, selectivelyreducing the chrominance values of the remaining identified white pixelsfor which at least one neighboring pixel is an identified white pixel;and for remaining identified black pixels with chrominance values notwithin the chrominance adjustment threshold of the chrominance neutralpoint, selectively reducing the chrominance values of the remainingidentified black pixels for which at least one neighboring pixel is anidentified black pixel.
 4. The method of claim 3: wherein selectivelyreducing the chrominance values of the remaining identified white pixelsfor which at least one neighboring pixel is an identified white pixelcomprises: for each chrominance axis, computing an average deviationfrom the neutral point chrominance neutral point for identified whiteneighboring pixels and the current white pixel, and selectivelyadjusting the individual chrominance values by an amount equal to eitherthe chrominance adjustment threshold or the average deviation from thechrominance neutral point for identified white neighboring pixels andcurrent white pixel; and wherein selectively reducing the chrominancevalues of the remaining identified black pixels for which at least oneneighboring pixel is an identified black pixel comprises: for eachchrominance axis, computing an average deviation from the chrominanceneutral point for identified black neighboring pixels and the currentblack pixel, and selectively adjusting the individual chrominance valuesby an amount equal to either the chrominance adjustment threshold or theaverage deviation from the neutral point for identified blackneighboring pixels and current pixel.
 5. The method of claim 4,comprising selectively further adjusting chrominance values of at leastone of the identified white and black pixels based on adjustedchrominance values of neighboring pixels.
 6. The method of claim 3,comprising selectively further adjusting chrominance values of at leastone of the identified white and black pixels based on adjustedchrominance values of neighboring pixels.
 7. The method of claim 1,comprising selectively further adjusting chrominance values of at leastone of the identified white and black pixels based on adjustedchrominance values of neighboring pixels.
 8. The method of claim 7,wherein further adjusting chrominance values comprises adjusting thechrominance values to the chrominance neutral point if the adjustedchrominance values of all the neighboring pixels are at the chrominanceneutral point.
 9. The method of claim 7, further comprising selectivelyfurther adjusting chrominance values of at least one of the identifiedwhite and black pixels to the chrominance neutral point if the adjustedchrominance values are within one of the chrominance neutral point. 10.The method of claim 1, further comprising selectively further adjustingchrominance values of at least one of the identified white and blackpixels to the chrominance neutral point if the adjusted chrominancevalues are within one of the chrominance neutral point.
 11. The methodof claim 1, further comprising storing adjusted pixel valuescorresponding to the image in a memory.
 12. The method of claim 1,further comprising: scanning an original document to produce ared-green-blue color pixel representation of an original image; andconverting values of red-green-blue pixels of the red-green-blue colorpixel representation into corresponding luminance-chrominance pixelvalues;
 13. The method of claim 1, further comprising identifyingnon-white and non-black pixels having chrominance values within a narrowchrominance threshold value of the chrominance neutral point; andselectively reducing the chrominance values of the identified non-whiteand non-black pixels based at least partially on chrominance of at leasttwo neighboring pixels if at least two neighboring pixels havechrominance values within the narrow chrominance threshold value of thechrominance neutral point and have luminance values within a narrowluminance threshold value of the current pixel luminance value.
 14. Adocument processing system, comprising: a scanning component operativeto produce a red-green-blue color pixel representation of an originalimage; a red-green-blue color space to luminance-chrominance color spaceconverter operative to convert values of red-green-blue pixels intocorresponding luminance-chrominance pixel values; a white and blackpixel identification component operative to identify white pixels havingluminance values within a white offset value of a whitepoint valueassociated with the image and having chrominance values within anon-zero white chrominance threshold value of a chrominance neutralpoint, and to identify black pixels having luminance values within ablack offset value of a blackpoint value associated with the image andhaving chrominance values within a non-zero black chrominance thresholdvalue of the chrominance neutral point; a chrominance value adjustmentcomponent operative to selectively reduce chrominance values of theidentified white and black pixels based at least partially on proximityto the chrominance neutral point and chrominance of at least oneneighboring pixel; and a memory for storing original and adjusted pixelvalues corresponding to the image.
 15. The document processing system ofclaim 14, wherein the white chrominance threshold value is greater thanthe black chrominance threshold value.
 16. The document processingsystem of claim 14, wherein the chrominance value adjustment componentis operative to selectively reduce the chrominance values of theidentified white and black pixels with chrominance values within achrominance adjustment threshold of the chrominance neutral point to thechrominance neutral point; to selectively reduce the chrominance valuesof remaining identified white pixels for which at least one neighboringpixel is an identified white pixel for remaining identified white pixelswith chrominance values not within the chrominance adjustment thresholdof the chrominance neutral point; and to selectively reducing thechrominance values of remaining identified black pixels for which atleast one neighboring pixel is an identified black pixel for remainingidentified black pixels with chrominance values not within thechrominance adjustment threshold of the chrominance neutral point; wherethe chrominance adjustment threshold is less than the white chrominancethreshold value and less than the black chrominance threshold value. 17.The document processing system of claim 16, wherein the chrominancevalue adjustment component is operative to selectively reduce thechrominance values of the remaining identified white pixels for which atleast one neighboring pixel is an identified white pixel by computingaverage deviations from the chrominance neutral point for identifiedwhite neighboring pixels and current white pixel, and selectivelyadjusting the individual chrominance values by an amount equal to eitherthe chrominance adjustment threshold or the average deviation from theneutral point for identified white neighboring pixels and current pixel;and wherein the chrominance value adjustment component is operative toselectively reduce the chrominance values of the remaining identifiedblack pixels for which at least one neighboring pixel is an identifiedblack pixel by computing an average deviation from the chrominanceneutral point for identified black neighboring pixels, and byselectively adjusting the individual chrominance values by an amountequal to either the chrominance adjustment threshold or the averagedeviation from the neutral point chrominance neutral point foridentified black neighboring pixels and current pixel.
 18. The documentprocessing system of claim 17, wherein the chrominance value adjustmentcomponent is operative to selectively further adjust chrominance valuesof at least one of the identified white and black pixels based onadjusted chrominance values of neighboring pixels.
 19. The documentprocessing system of claim 16, wherein the chrominance value adjustmentcomponent is operative to selectively further adjust chrominance valuesof at least one of the identified white and black pixels based onadjusted chrominance values of neighboring pixels.
 20. The documentprocessing system of claim 14, wherein the chrominance value adjustmentcomponent is operative to selectively further adjust chrominance valuesof at least one of the identified white and black pixels based onadjusted chrominance values of neighboring pixels.
 21. The documentprocessing system of claim 20, wherein the chrominance value adjustmentcomponent 160) is operative to further adjust chrominance values byadjusting the chrominance values to the chrominance neutral point if theadjusted chrominance values of all the neighboring pixels are at thechrominance neutral point.
 22. The document processing system of claim14, wherein the chrominance value adjustment component 160) is operativeto further identify non-white and non-black pixels having chrominancevalues within a narrow chrominance threshold value of the chrominanceneutral point, and to selectively reduce the chrominance values of theidentified non-white and non-black pixels based at least partially onchrominance of at least two neighboring pixels if at least twoneighboring pixels have chrominance values within the narrow chrominancethreshold value of the chrominance neutral point and have luminancevalues within a narrow luminance threshold value of the current pixelluminance value.